Poly(phenylene ether)s are a class of plastics having excellent water resistance, thermal resistance, and dimensional stability. They retain their mechanical strength in hot, and/or wet environments. Therefore they can be used for the fabrication of porous asymmetric membranes useful in various separation processes. For example, poly(phenylene ether)s can be used in processes that require repeated cleaning with hot water or steam sterilization. However the use of poly(phenylene ether)s in various water treatment processes can be limited because of their hydrophobicity. The membranes are not wettable by water, and a high pressure gradient is required to pass water through the membrane pores. Moreover, hydrophobic interactions between the membrane and solutes in feed streams can cause membrane fouling, which adversely affects membrane performance, and requires cleaning or membrane replacement.
The surface of membranes fabricated from hydrophobic polymers can be made hydrophilic by blending with a hydrophilic polymer. For example, polyethersulfone can be blended with poly(N-vinylpyrrolidone), and the two polymers can be co-precipitated from solution to form a membrane. However, excess poly(N-vinylpyrrolidone) must be washed off of the membrane with water, which results in a waste of valuable material, and which produces an aqueous waste comprising the excess poly(N-vinylpyrrolidone). Moreover the hydrophilic polymer can be leached out of the membrane in membrane treatment of aqueous streams. There remains a need for a polymer that provides a hydrophilic surface to porous asymmetric membranes fabricated from hydrophobic polymers. The polymer should be hydrophilic and still have an affinity for the hydrophobic polymer, so that it is not extracted by washing during fabrication or in end-use operation of the membrane.